Characterisation of a Peptidase from Lactococcus lactis ssp cremoris HP that Hydrolyses Di- and Tripeptides Containing Proline or Hydrophobic Residues as the Aminoterminal Amino Acid

An intracellular peptidase, showing highest catalytic activity towards di- and tripeptides containing proline and to a lesser extent other hydrophobic residues as the amino-terminal amino acid, was purified from cell-free extracts of Lactococcus lactis ssp. cremoris HP. On SDS-PAGE the enzyme exhibited a molecular mass of 50 kDa. In HPLC gel filtration experiments, an apparent molecular mass of approximately 110 kDa was observed. The activity of the enzyme was inhibited by EDTA, dithiothreitol and some metal ions, but was not affected by PMSF, aprotinin or pepstatin. After inhibition with EDTA the activity could be restored by Co ++ and Mn ++. The optima for pH, temperature and NaCl concentration are 8.5, 37°C and 100 mM respectively. The Michaelis constant (K m) and V max for several proline-containing di- and tripeptides were determined.